Houthi militia forces are tightening their grip on southern Yemen

Houthi fighters ride a patrol truck in Sanaa March 25, 2015. REUTERS/Khaled Abdullah ADEN (Reuters) - Houthi militia forces and allied army units seized Aden airport and a nearby air base on Wednesday, tightening their grip on the outskirts of the southern Yemeni city after President Abd-Rabbu Mansour Hadi fled his residence for a safer location.

The United States said Hadi, holed up in Aden since fleeing the Houthi-controlled capital Sanaa last month, was no longer at the compound he has been using as a base. It offered no other details on his movements.

"We were in touch with him earlier today," State Department spokeswoman Jen Psaki told a briefing in Washington. "He is no longer at his residence. I'm not in position to confirm any additional details from here about his location."

Residents later said looters had entered the residence hours after Hadi vacated it in mid-afternoon for an unknown location. Foreign Minister Riyadh Yaseen and Hadi's aides said Hadi remained in Aden, in a safe place, without elaborating.

Local officials said troops loyal to Yemen's ex-president Ali Abdullah Saleh, a powerful ally of the Houthis, had captured Aden airport in late afternoon but that clashes with Hadi supporters were continuing in the vicinity. The airport was closed and all flights were canceled.

Earlier the Houthis and their allies took al-Anad air base 60 km (37 miles) north of the city before continuing their southward advance.

People seek shelter during a gunfire at an army base in Yemen's southern port city of Aden March 25, 2015. REUTERS/Anees Mansour Yemen's slide toward civil war has made the country a crucial front in mostly Sunni Saudi Arabia's rivalry with Shi'iteIran, which Riyadh accuses of stirring up sectarian strife through its support for the Houthis.

Sunni Arab monarchies around the region have condemned the Shi'ite Houthi takeover as a coup and have mooted a military intervention in favor of Hadi in recent days.

U.S. officials say Saudi Arabia is moving heavy military equipment including artillery to areas near its border with Yemen, raising the risk that the Middle East's top oil power will be drawn into the worsening conflict.

A Southern People's Resistance militant loyal to Yemen's President Abd-Rabbu Mansour Hadi mans an anti-aircraft machine gun the militia seized from the army in al-Habilin, in Yemen's southern province of Lahej March 22, 2015. REUTERS/Nabeel Quaiti Saudi sources said the build-up, which also included tanks, was purely defensive.

Soldiers at Aden's Jabal al-Hadeed barracks fired into the air to prevent residents from entering and arming themselves, witnesses said, suggesting that Hadi's control over the city was fraying. Five people were killed and 12 wounded in shooting at the barracks, medical sources said without elaborating.

Earlier, unidentified warplanes fired missiles at the Aden neighborhood where Hadi's compound is located, residents said. Anti-aircraft batteries opened fire on the planes.

Southern People's Resistance militants loyal to Yemen's President Abd-Rabbu Mansour Hadi take positions on the frontline of fighting against Houthi fighters in the country's southern province of Lahej March 24, 2015. REUTERS/Nabeel Quaiti While the battle for Aden is publicly being waged by the Houthi movement, many there believe that the real instigator of the campaign is former president Saleh, a fierce critic of Hadi.

Saleh was the force behind Aden's previous humiliation in 1994, when as president he crushed a southern secessionist uprising in a short war.

Unlike other regional leaders deposed in the Arab Spring, Saleh was allowed to remain in the country.

Army loyalists close to Saleh on Wednesday warned against foreign interference, saying on his party website thatYemen would confront such a move "with all its strength".

Diplomats say they suspect the Houthis want to take Aden before an Arab summit this weekend, to preempt an expected attempt by Hadi ally Saudi Arabia to rally Arab support at the gathering for military intervention in Yemen.

The Arab League will discuss on Thursday a proposal by Yemen's foreign minister, who called on Arab states to intervene militarily to halt the Houthi advance, the regional body's deputy secretary general said.

The Houthi advance was taking its toll. The bodies of fighters from both sides lay on the streets of the outskirts of Houta, capital of Lahej province north of Aden, residents said.

Houthi rebels ride a truck in Sanaa February 15, 2015. Tens of thousands of Yemenis demonstrated in several cities on Saturday against the rule of the Shi'ite Muslim Houthi movement as clashes between Houthis and Sunnis in a southern mountainous region left 26 dead. Reuters In Houta, storefronts were shuttered and residents reported hearing bursts of machine gun fire and saw the bodies of fighters from both sides lying in the streets.

Witnesses said Houthi fighters and allied soldiers largely bypassed the city center and traveled by dirt roads to the southern suburbs facing Aden.

Heavy traffic clogged Aden as parents brought schoolchildren home and public sector employees obeyed orders to leave work. Witnesses said pro-Hadi militiamen and tribal gunmen were out in force throughout the city.

"The war is imminent and there is no escape from it," said 21-year-old Mohammed Ahmed, standing outside a security compound in Aden's Khor Maksar district, where hundreds of young men have been signing up to fight the advancing Shi'ite fighters.

"And we are ready for it.

A frontal view of a tank barrel is seen as Shi'ite Houthi rebels stand on its turret, after they took over the compound of the army's First Armoured Division in Sanaa September 22, 2014 Khaled Abdullah Ali Al Mahdi/REUTERS Houthi militants took control of Sanaa last September and seized the central city of Taiz at the weekend as they moved closer to Aden.

Houthi leaders have said their advance is a revolution against Hadi and his corrupt government. Iran has blessed their rise as part of an "Islamic awakening" in the region.